To date, the standard method to access a mouse tail vein is manual injection, but its yield rate is poor in general. This leads to multiple needle insertions associated with tissue damage and pain. Besides, failure in tail-vein injection leads to data loss, and thereby more animals will be required to compensate it. Finally, the dose variation induced by unreliable injection increases errors in data quantification. Therefore, the development of a portable and inexpensive device presenting high yield rate is imperative to improve animal welfare and data quality and to reduce the total research cost. The PI has recently invented a device to facilitate tail-vein injection in mice, named Mouse Tail-vein Injection Needle Guide (MTING). MTING guides a needle to the lateral tail vein of a mouse using the relationship between the tail diameter and the vein depth. MTING also contains a light emitting diode (LED) to visualize the tail vein regardless of mouse skin color. Using MTING, the PI achieved 87% yield rate (13 out of 15 animals). MTING is small and made of inexpensive materials, thus it can be globally affordable for routine preclinical research. However, proper training for hand posture and mouse-tail positioning is required for using MTING, thus its yield rate can be still affected by the level of user training and experience. The goal of this Phase I proposal is to upgrade MTING so that the high yield rate can be achieved regardless of training and experience level of technicians. Three specific aims over a 12-month period are proposed as follows. Aim 1: Develop mouse tail holders. Mouse-tail holders will secure the tail firmly, while yielding the appropriate amount of pressure to dilate the vein. This is important especially when the animals are not anesthetized. Aim 2: Develop an automatic illumination system. In the upgraded version, the LED will be turned on automatically, only when the mouse tail is properly positioned. Therefore, the LED will function not only for visualizing tail vein but also as an indicator of proper tail positioning. Aim 3: Validate the upgraded device in preclinical settings. The MTING equipped with the new mouse tail holders and automatic illumination system will be tested in three strains of laboratory mice: black, agouti, and albino. Each mouse will be injected with green dye using the MTING (test group) or following the conventional protocol (control group), and the yield rates achieved by two different methods will be statistically compared. MTING will be also tested for blood withdrawal.